A FUNGUS INFECTING DOMESTIC FLIES MANIPULATES SEXUAL-BEHAVIOR OF ITS HOST

The entomopathogenic fungus Entomophthora muscae infects and kills dom estic flies Musca domestica, and rates of transmission are higher at h igh population densities. I tested whether features of parasitized hos ts increased the likelihood of transmission of the fungus in a series of experiments. Individual flies contacting an infected conspecific ha d a much higher probability of becoming infected than had flies contac ting a dead fly without signs of infection. Males especially were attr acted to and behaved sexually towards dead, infected flies even when a choice was available between a dead, infected fly and a dead, uninfec ted individual. The abdomen of infected flies swelled considerably as a consequence of infection, and uninfected female flies with larger ab domens are more fecund than the average female and maybe more attracti ve. Experiments in which abdomens of infected and uninfected flies wer e cut off and glued back on other flies demonstrated that the abdomens of infected flies were highly attractive to males. When the size of t he abdomen of infected and uninfected individual flies was held consta nt, infected dead flies were still more attractive than corpses of uni nfected flies. This result suggests that features other than the size of the swollen abdomen enhanced the attractivity of infected flies. Fe atures of infected hosts therefore increased the likelihood of transmi ssion of the parasitic fungus.